1. Field of the Invention
The present invention relates to a charging device for an electronic timepiece having a generator for receiving at least one type of external energy and converting the external energy into electric energy and a charge storer for storing the electric energy generated by the generator. The present invention further relates to an electronic timepiece using such a charging device, and a method for controlling the charging device.
2. Description of the Related Art
A small-sized electronic timepiece such as a wristwatch has a time-keeping circuit for measuring time and a timepiece driving circuit including a driving circuit for driving a motor which is coupled to a hand moving mechanism, i.e., a mechanism to move hands of the timepiece. Electronic timepieces having a generator therein have been realized in the art, which can operate without having to replace a used battery.
In these electronic timepieces, the electric power generated by the generator can be once charged into a secondary power source such as a capacitor. Therefore, when no electric power is being generated, time display is performed by the electric power which is discharged from the secondary power source. This enables the timepiece to stably operate over a long period of time without a battery.
In view of the labor and time for replacing a used battery or the problems associated with the disposal of used batteries, it is expected that more electronic timepieces will be provided with a generator in the future.
Generators which are provided in a timepiece such as a wristwatch include a solar battery which converts incident light into electric energy, a power generation system which converts kinetic energy of the movement of the user""s arm into electric energy, etc.
These generators are quite desirable in that they can utilize energy around the user by converting it into electric energy. However, the available energy density is small, and the energy cannot be obtained continuously. Therefore, power is not generated continuously. During the non-power-generation periods (i.e., when the generator is in an inoperative state), the electronic timepiece is operated by the electric power which has been stored in the secondary power source.
In the case of an electronic device with a solar battery installed, for example, no electric power is generated by the solar battery in the nighttime. In such an electronic device with a solar battery installed, a charge storer discharges to operate a processing device. Therefore, it is desired to increase the storage capacity of the charge storer so as to accommodate situations where no electric power is generated by the power generation system. However, an increase in the storage capacity of the charge storer also increases the time required to charge the capacitor device. As a result, once the capacitor device is completely discharged off, it then takes a long time for the capacitor device to be charged to a predetermined voltage sufficient to operate the processing device. Thus, once a device employing a solar battery stops operating, for example, it will take some time to start up the device even after the device is placed back into an environment where light is incident upon the solar battery and the power generation has been resumed.
A number of circuits have been devised in the art to shorten the processing device start-up time in such situations.
An example of such circuits is shown in FIG. 8 which is a block diagram illustrating portable electronic equipment (an electronic timepiece) having a solar battery as described in Japanese Patent Provisional Publication No. 9-264971, entitled xe2x80x9cPower Control Device, Power Generation Device and Electronic Equipmentxe2x80x9d.
In FIG. 8, the electronic timepiece includes a solar battery 501, a capacitor device 513, and a power control section 520.
The solar battery 501 converts energy of the sunlight into electric power.
The capacitor device 513 stores the electric power from the solar battery 501.
The power control section 520 supplies the electric power from the solar battery 501 to the large-capacity capacitor device 513 and to a processing device 509 such as a time-keeping device.
The capacitor device 513 will now be described in detail.
The capacitor device 513 includes a capacitor 502, diodes 517, 521, 522 and 529, switches 518, 523 and 524, a limit switch 519, and a control circuit 530.
The capacitor 502 is a large-capacity capacitor such as an electric doublelayer capacitor.
The switch 523 is coupled between the ground power rail (which in the present case is used as the reference high voltage VDD) and the anode of diode 522. When switch 523 is actuated (i.e. is closed) it forms a bypass current path around diode 521. Diodes 521 and 522 are coupled end-to-end such that when switch 523 is not actuated (i.e. is opened), diodes 521 and 522 are effectively serially connected with each other. In the electronic timepiece illustrated in FIG. 8, the reference high voltage VDD is the ground voltage power rail (reference voltage), and the VSS line is the relative low voltage. To emphasize that VDD is implemented by the ground power rail, the term xe2x80x9cground voltage VDDxe2x80x9d is at times used to refer to the reference high source, i.e. high side, of the circuit.
The switch 524 is coupled between the VDD voltage and the cathode of diode 522. When switch 524 is actuated (i.e. is closed), it forms a bypass current path around both of the diodes 521 and 522.
The diode 529 is provided between the solar battery 501 and one of the terminals of the capacitor 502 which is on the VSS voltage (low voltage) side. The diode 529 functions as a reverse current flow prevention diode. Specifically, the diode 529 is operative to ensure that a voltage which is discharged from the capacitor 502 while no power is being generated from the solar battery 501 is not applied to the solar battery 501.
The diode 517 is operative to ensure that a current does not flow in the reverse direction from an auxiliary capacitor device 516 including a small-capacity capacitor 503 to the solar battery 501.
The switch 518 is a switch provided for controlling a discharge from the capacitor device 513 into the auxiliary capacitor device 516.
The limit switch 519 short-circuits the high voltage side VDD and the low voltage side VSS with each other when the voltage supplied from the solar battery 501 is too high. In this way, it is possible to prevent the capacitor device 513 from being overcharged so that a high voltage is not applied to the processing device 509, etc.
The control circuit 530 monitors various voltages in the power control section 520 and controls the switches. The control circuit 530 detects a voltage VSCP on the high voltage side of the capacitor device 513, a voltage VSCN on the low voltage side of the capacitor device 513, the voltage VSS which is supplied to the processing device 509, etc.
Based on the detection results, the control circuit 530 outputs control signals for controlling the switch 523 and the switch 524, respectively. The control circuit 530 also outputs a control signal for controlling the switch 518 (which is provided for controlling the discharge from the capacitor device 513 into the auxiliary capacitor device 516), and a control signal for controlling the limit switch 519.
With the configuration as described above, a charge voltage VSC of the capacitor device 513 is equal to the difference between the terminal voltages thereof, i.e., between the high potential side voltage VSCP and the low potential side voltage VSCN. However, when light is illuminated onto the solar battery 501 while substantially no electric charge is stored in the capacitor device 513 and the charge voltage VSC is substantially 0 V, the switches 523 and 524 are turned OFF.
Therefore, the electric power supplied from the solar battery 501 is dropped by a forward bias voltage of the diodes 521 and 522. Thereafter, the electric power is supplied to the capacitor device 513. Thus, a voltage drop is caused by the diodes 521 and 522.
In this way, it is possible to increase the voltage to be applied to the processing device 509 by an amount corresponding to the voltage drop.
As the charge voltage VSC of the capacitor 502 gradually increases and reaches a predetermined setting voltage, the switch 523 and the switch 524 are sequentially turned ON. Thus, the diodes 521 and 522 are bypassed, thereby increasing the charge voltage VSC to the capacitor 502.
In the conventional example shown in FIG. 8, two diodes 521 and 522 are used in order to increase the voltage to be applied to the processing device 509. However, in alternative circuit configurations, resistive elements may be used in place of the diodes 521 and 522 (see, for example, U.S. Pat. Nos. 5,001,685 and 4,730,287).
In the above-described conventional example, a voltage decreasing means such as a diode, a resistor, or the like, is provided between a capacitor, which is used as the secondary power source, and the ground voltage VDD in order to increase the voltage applied to the processing device such as a timepiece driving circuit at the beginning of power generation. Moreover, a line is provided and connected to the terminals of the capacitor for detecting the charge voltage of the capacitor (the voltage between VSCP and VSCN in FIG. 8).
In such a configuration, it is necessary to isolate one of the terminals of the secondary power source (terminal A in FIG. 8) from the ground voltage VDD. In addition, it is necessary to provide a power supply line for supplying the voltage at terminal A while isolating the power supply line from the ground voltage VDD to a circuit board mounting thereon a control circuit, a timepiece driving circuit, and the like.
FIG. 9 is a partial cross-sectional view illustrating how a circuit board is placed in an electronic timepiece.
In FIG. 9, a secondary power source (the capacitor 502) is provided separately from a circuit board 601. The terminal A of the capacitor 502 is connected to a predetermined contact point on the circuit board 601 by a connection member 602, e.g., a contact point spring, or the like.
A circuit hold plate 603 for holding down the circuit board 601 is made of an electrically conductive material such as a stainless having a potential equal to the ground voltage VDD.
A circuit spacer 604 is made of an insulating member. The circuit spacer 604 and the circuit hold plate 603 together sandwich the circuit board 601 therebetween.
The circuit board 601 is secured by a press-fit member 605, which is press-fit through the circuit spacer 604, and a screw 606.
A circuit insulating plate 607 is provided between the circuit board 601 and the circuit hold plate 603. The circuit insulating plate 607 is made of an insulating material. The circuit insulating plate 607 insulates lines on the circuit board 601 from the ground voltage VDD.
A base plate 608 is secured to the circuit spacer 604 by the press-fit member 605.
The base plate 608 is further secured by a circuit case.
With the configuration as described above, where one of the terminals (terminal A) of the secondary power source (the capacitor 502) is connected to the predetermined contact point on the circuit board 601 by a contact point spring (the portion indicated by a broken line 602), or the like, the power source potential of the secondary power source may be instable.
This is because the contact resistance of the electrically conductive member varies due to a shock.
Moreover, it is necessary to ensure a sufficient ground space on the circuit board 601 to insulate signal lines and grounded points from the power supply line of the secondary power source by providing an insulating mechanism or a sufficient creepage distance. This has prevented the size of the circuit board 601 from being reduced. Therefore, it has not been possible to employ such a voltage-increasing configuration as described above in a small analog electronic timepiece for women.
Moreover, the positive terminal A of the secondary power source has a voltage that is different than the ground voltage VDD. Therefore, it is not possible to directly connect the positive terminal A of the secondary power source and the connection member 602 to the grounded points. Furthermore, it is necessary to provide the insulating member for providing an insulation from the contact point.
Moreover, as illustrated in FIG. 8, a circuit for causing a voltage drop is provided by using a diode. In such a case, no current flows through the diodes 521 and 522 while the switches 523 and 524 are OFF and no electric power is being generated. Therefore, the terminal and lines for detecting the voltage VSCP are brought into a high impedance state and thus are more likely to be influenced by noise.
In view of the above, an object of the present invention is to provide a charging device for an electronic timepiece having a function of boosting the voltage at the beginning of power generation, an electronic timepiece using such a charging device, and a method for controlling the charging device. The present invention also aims to allow the ground voltage side terminal of the secondary power source to be grounded directly.
In accordance with an aspect of the present invention, an electronic timepiece charging device for charging an electronic timepiece comprises: a generator for receiving at least one type of external energy and converting the external energy into electric energy; a capacitor device for storing the electric energy generated by said generator; a timepiece circuit connected in parallel to said capacitor device for performing a time-keeping operation, said timepiece circuit being driven by the electric energy generated by said generator or the electric energy stored in said capacitor device; and a display circuit for displaying time information from said timepiece circuit, wherein:
said timepiece circuit is connected in parallel to said capacitor device;
said capacitor device comprises an equivalent capacitive component for storing an electric charge and a resistive component formed by a part of said equivalent capacitive component; and
a resistance value of said resistive component is set in such manner that when the generator outputs a current equal to or greater than a predetermined value by means of a voltage drop caused by a charging current of said resistive component, a voltage to be applied to said timepiece circuit by the generator is equal to or greater than a voltage at which said timepiece circuit starts operating.
Preferably, said resistive component has a resistance value which is equal to or greater than a value obtained by dividing an operation starting voltage of the timepiece circuit by a current generated by said generator, or a value obtained by first subtracting a remaining charge voltage of said capacitor device at a time when the timepiece circuit stops operating from the operation starting voltage of the timepiece circuit to obtain a difference therebetween, and then dividing said difference by the current generated by said generator.
Preferably, said generator comprises a photoelectric power generator, a magnetoelectric power generator, a thermoelectric power generator, or a piezoelectric power generator.
Preferably, said capacitor device equivalently comprises one capacitive component and one resistive component which are serially connected with each other.
Preferably, said capacitor device equivalently comprises a plurality of pairs of capacitive components and resistive components which are connected in parallel to one another, each pair having one capacitive component and one resistive component which are serially connected with each other.
Preferably, said capacitor device is a lithium secondary battery comprising an electrolytic solution of an organic solvent having a lithium salt dissolved therein, a negative pole activator using titanium oxide, and a positive pole activator using manganese oxide.
Preferably, said capacitor device is a lithium secondary battery comprising an electrolytic solution of an organic solvent having a lithium salt dissolved therein, a negative pole activator using a carbon material, and a positive pole activator using lithium titanate.
Preferably, wherein said capacitor device comprises an electrolytic capacitor.
Preferably, said generator comprises an AC generator, and a charging time constant of said capacitor device is less than or equal to one cycle of a half-wave- or full-wave-rectified waveform of a current generated by said AC generator.
Preferably, one terminal of said capacitor device is grounded to a ground potential which is common among said generator, said timepiece circuit and said capacitor device.
Preferably, one terminal of said capacitor device is grounded to an electrically conductive attachment member having said ground potential.
In accordance with another aspect of the present invention an electronic timepiece comprises:
a generator for receiving at least one type of external energy and converting the external energy into electric energy;
a capacitor device for storing the electric energy generated by said generator;
a timepiece circuit connected in parallel to said capacitor device for performing a time-keeping operation, said timepiece circuit being driven by the electric energy generated by said generator or the electric energy stored in said capacitor device;
a display circuit for displaying time information from said timepiece circuit; and
the above-described charging device.
In accordance with another aspect of the present invention, a method for controlling a charging device for an electronic timepiece is provided. The charging device includes a generator for receiving at least one type of external energy and converting the external energy into electric energy; a capacitor device for storing the electric energy generated by said generator; a charging device for charging said capacitor device; a timepiece circuit connected in parallel to said capacitor device for performing a time-keeping operation, said timepiece circuit being driven by the electric energy generated by said generator or the electric energy stored in said capacitor device; and a display circuit for displaying time information from said timepiece circuit. The method comprises:
connecting the timepiece circuit in parallel to said capacitor device;
forming said capacitor device by an equivalent capacitive component for storing an electric charge and a resistive component formed by a part of said equivalent capacitive component; and
setting a resistance value of the resistive component in such manner that when said generator outputs a current equal to or greater than a predetermined value by means of resistance value of said resistive component, a voltage to be applied to said timepiece circuit by said generator is equal to or greater than a voltage at which said timepiece circuit starts operating.
In accordance with another aspect of the present invention, an electronic timepiece charging device comprises:
a generator for receiving at least one type of external energy and converting the external energy into electric energy; a capacitor device for storing the electric energy generated by said generator; a timepiece circuit connected in parallel to said capacitor device for performing a time-keeping operation, said timepiece circuit being driven by the electric energy generated by said generator or the electric energy stored in said capacitor device; and a display circuit for displaying time information from said timepiece circuit, wherein:
said timepiece circuit is connected in parallel to said capacitor device;
said capacitor device comprises at least an equivalent capacitive component for storing an electric charge and a resistive component; and
where a voltage in said capacitor device to be supplied to said timepiece circuit is less than an operation starting voltage of said timepiece circuit, and when said timepiece circuit has stopped operating and in addition when a charging current flows into said capacitor device due to power generation by said generator, said the capacitor device supplies to said timepiece circuit a voltage which is equal to or greater than the operation starting voltage of said timepiece circuit by utilizing at least a voltage difference caused by said resistive component.
In accordance with another aspect of the present invention, a method for controlling a charging device for an electronic timepiece including: a generator for receiving at least one type of external energy and converting the external energy into electric energy; a capacitor device for storing the electric energy generated by said generator; a timepiece circuit connected for performing a time-keeping operation, said timepiece circuit being driven by the electric energy generated by said generator or the electric energy stored in said capacitor device; and a display circuit for displaying time information from said timepiece circuit. The method comprises:
connecting said timepiece circuit in parallel to said capacitor device;
forming said capacitor device by at least an equivalent capacitive component for storing an electric charge and a resistive component; and
where a voltage in said capacitor device to be supplied to said timepiece circuit is less than an operation starting voltage of said timepiece circuit, and when said timepiece circuit has stopped operating and in addition when a charging current flows into said capacitor device due to power generation by said generator, controlling said capacitor device to supply to said timepiece circuit a voltage which is equal to or greater than the operation starting voltage of said timepiece circuit by utilizing at least a voltage difference caused by said resistive component.